1. Field of the Invention
The present invention relates to a tone generating apparatus, for the production of tone signals, that is intended for use in such electronic musical instruments as electronic keyboards, electronic pianos, and synthesizers.
Currently, various electronic musical instruments have been developed and are in practical use. Each such electronic musical instrument incorporates a tone generating apparatus and generates musical tones with a variety of timbres that correspond to a player's selection.
A desirable characteristic for an electronic musical instrument is that it produce clear musical tones with as little extraneous noise as possible.
2. Description of the Related Art
Well known in the conventional art is a tone generating apparatus that employs, for the production of musical tones, a read-out system that sequentially acquires tone waveform data, which has previously been stored in a memory, and uses the acquired data to reproduce tone signals.
For a musical tone, a tone generating apparatus that employs such a read-out system stores in a memory, as tone waveform data, a rising portion of a musical tone and a succeeding repetitive portion. To produce a sustained tone signal, such a tone generating apparatus reads the tone waveform data that correspond to the rising portion and the repetitive portion once, and then iteratively reads the tone waveform data for the repetitive portion.
When tone waveform data for the repetitive portion is iteratively read with this system, however, it is difficult to exactly read a predetermined cycle. Also, while data for the repetitive portion are being iteratively read, discontinuities occur at the junctures of the repeated cycles. As these discontinuities interrupt the smooth flow of musical tones and interject unnecessary harmonic overtones, the quality of the musical tones that are produced is degraded.
As shown in FIG. 8, for example, when one cycle of a sinusoidal waveform is employed as a repetitive portion, during iterative data reading improper extraction of a tone signal causes a discontinuity N.
When a sinusoidal waveform that has no discontinuities, as shown in FIG. 5, is employed, its spectrum is as depicted in FIG. 6 and a clear musical tone, which includes only a frequency component of the associated tone signal, is obtained.
However, as shown by the spectrum in FIG. 9, a waveform with discontinuities N, such as is depicted in FIG. 8, has multiple unwanted harmonic overtones that are not included in the original waveform.